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Sensors odbiciowe
There are many types of sensors used in automation and robotics. Gas sensors, light sensors, touch and motion sensors – these are just some of the types, probably the most popular ones. However, one of the most interesting modules extending a given project with a number of new functions are reflection sensors.
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Principle of operation and connection of reflective sensors
One of the simplest implementations of an optical sensor is an infrared LED paired with a phototransistor. The phototransistor is connected to the supply voltage source through a resistor that forms a voltage divider. At the output of this divider, a voltage ranging from 0V to typically 5V is obtained as a representation of the infrared reflection, with a smaller value representing a stronger infrared reflection. The analog output of the sensor, providing the received voltage, can be connected for further reading in various ways. The easiest way to do this is to connect the sensor output to the analog input of the ADC converter in the microcontroller or to the binary input using a software comparator. There is also a solution of connecting the sensor to a hardware comparator with an adjustable threshold for changing the logical state (e.g. LM393 integrated circuit). The state at the comparator output is then read at the microcontroller's binary input. Due to the small size of the sensors, they can be easily connected in parallel in the form of a strip, which allows for easy detection of edges, walls and other obstacles, including the ability to measure the distance from them.
Measurement accuracy of reflective sensors
Solutions such as a laser sensor or an optoelectronic sensor have sufficiently good measurement accuracy and work well in many hobby projects. However, to obtain the best possible accuracy of the sensor in the application in which it will be used, it must be calibrated. Calibration of a proximity sensor is an important process because there are no perfect measurement sensors and, despite the repeatable production technology, two identical sensors may output different voltage values, even if they work in the same environmental conditions. The materials from which sensors are made also go through natural aging processes, which requires their periodic recalibration. It is best to perform calibration in software, e.g. in the Arduino program code working with the sensor. The ideal calibration of the sensor is when the measured distance value corresponds to the voltage at the sensor output approximately in direct proportion.
Reflective sensors - FAQ
Reflective sensors are used in industrial automation. A special application of reflective sensors are linefollower robots that follow a line painted on a given surface (e.g. the floor). The operation of reflective sensors is based on the phenomenon of interrupting the light flux that is sent from the sensor and then reflected by the reflector. Depending on the specific type of reflectance sensor, these electronic components use light that is invisible to the human eye (e.g. ultraviolet or infrared rays) or visible light. A common feature of reflective sensors is the transmitter and receiver enclosed in one housing. The state in which the light stream is interrupted changes the signal output from the sensor.
Reflective sensors are used, among others, in industrial automation. They are installed in linefollower robots, whose main task is to follow a painted line (e.g. on a warehouse floor). The principle of operation of reflectivity sensors is to emit light and reflect it using a reflector. When the light stream is interrupted, the signal changes.